From the prior art, hybrid vehicles comprising a hybrid transmission are known. In addition to the internal combustion engine they comprise at least one electric motor or electric machine. In serial hybrid vehicles a generator is driven by the internal combustion engine, the generator supplying the electric motor that drives the wheels with electrical energy. Furthermore, parallel hybrid vehicles are known, in which the torque of the internal combustion engine and of at least one electric machine that can be connected to the internal combustion engine are added together. In this case the electric machines can be connected to the belt drive or to the crankshaft of the internal combustion engine. The torques produced by the internal combustion engine and/or the at least one electric machine are transmitted to the driven axle by a downstream transmission.
For example, from DE 102006019679 A1 a drivetrain with an electrically adjustable hybrid transmission and an electro-hydraulic control system, a plurality of electric power units and a plurality of torque transmission mechanisms is known. In this the torque transmission mechanisms can be selectively engaged by the electro-hydraulic control system to provide four forward gears, a neutral condition, an electrically adjustable operating mode with lower and higher rotation speeds, and an uphill operating mode.
From DE 102005057607 B3 a hybrid drive for vehicles is known, which contains at least a main motor, in particular an internal combustion engine, a generator, an electric motor and a planetary transmission comprising a sun gear, an ring gear, a planetary gear carrier and planetary gearwheels, which has at least one drive output shaft. In this case it is provided that in a first driving range of the vehicle, to add the torques, the drive output shafts of the main motor and the electric motor are coupled to the sun gear of the planetary transmission, and for a further driving range one of the two motors can be coupled with friction force locking to the ring gear of the planetary transmission in accordance with the superimposition principle for the mechanical addition of the rotation speeds.
In a vehicle with hybrid drive, in accordance with the prior art the motor is switched off when or immediately before the vehicle is at rest, to reduce the fuel consumption of the internal combustion engine.
From US 2005/0221947 A1 a drive control system for a hybrid motor vehicle is known, which comprises an internal combustion engine, a transmission with discrete transmission ratios, an electric machine arranged between the internal combustion engine and the transmission, and a first and a second clutch which can be actuated selectively in order to control the connection of the rotor of the electric machine to the transmission or to the internal combustion engine. In addition, this known drive control system comprises a control device for controlling the internal combustion engine, the electric machine and the clutches, which is designed to perform a start-stop function in which, during a stop phase, the internal combustion engine is separated from the electric machine and the transmission, and switched off.
In a subsequent start phase the connection of the electric machine working as an electric motor to the transmission is formed while a first transmission ratio is engaged in the transmission, so that the vehicle is at first driven by the electric machine. Then a shift from the first transmission ratio to a second, higher transmission ratio is carried out, and during this shift the connection of the internal combustion engine to the electric machine is formed, whereby the internal combustion engine is started. In addition it is provided that while the higher transmission ratio is engaged in the transmission, the connection between the electric machine and the transmission is broken by disengaging the corresponding clutch, which results in an interruption of the traction force. In a subsequent step the connection between the internal combustion engine and the transmission is formed, so that when the start phase has ended the vehicle is being driven by the internal combustion engine and optionally by the electric machine.